The present disclosure relates to electronic systems and methods, and in particular, to switching resonator filter circuits and methods.
Filter circuits are used in a wide range of electronic applications. Filter circuits are typically used as stages in a signal path to allow some frequency components of a signal to pass through the filter while other frequencies are attenuated by the filter. One common example filter is an LRC filter shown in FIG. 1. An LRC filter includes an inductor L, resistor R, and a capacitor C. An LRC filter may be used as a band pass filter, where a range of frequencies within the “pass band” are allowed to pass while frequencies above and below the pass band are attenuated. The pass band is typically centered around a “center frequency,” which in the case of an LRC circuit is ωo=1/sqrt(LC). In practical implementations, edges of the pass band are set according to frequencies above and below the center frequency where the attenuation increases to 3 dB.
Filters are often characterized in terms of “quality factor” or “Q”. Quality factor describes a resonators bandwidth relative to the center frequency (e.g., Q=fo/Δf, where fo is the center frequency in Hertz and Δf is the width of the pass band (or bandwidth) of the filter. For the parallel LRC filter in FIG. 1, for example, the quality factor is Q=R*sqrt(C/L). In this case, increasing R increases Q. However, in practical applications achieving high Q using passive components, such as resistors, would result in large circuit areas, high losses, and reduced circuit efficiency. High quality factor circuits are desirable to pass desired frequency components while attenuating other unwanted frequency components that may be close in frequency to the desired frequency components. It would be advantageous to achieve alternatives to typical L, R, and C filtering with very high quality factor filters.